Air and fuel supply system for combustion engine

ABSTRACT

A method of operating an internal combustion engine, including at least one cylinder and a piston slidable in the cylinder, may include supplying pressurized air from an intake manifold to an air intake port of a combustion chamber in the cylinder, selectively operating an air intake valve to open the air intake port to allow pressurized air to flow between the combustion chamber and the intake manifold substantially during a majority portion of a compression stroke of the piston, and operably controlling a fuel supply system to inject fuel into the combustion chamber after the intake valve is closed.

TECHNICAL FIELD

[0001] The present invention relates to a combustion engine and, moreparticularly, to an air and fuel supply system for use with an internalcombustion engine.

BACKGROUND

[0002] An internal combustion engine may include one or moreturbochargers for compressing a fluid, which is supplied to one or morecombustion chambers within corresponding combustion cylinders. Eachturbocharger typically includes a turbine driven by exhaust gases of theengine and a compressor driven by the turbine. The compressor receivesthe fluid to be compressed and supplies the compressed fluid to thecombustion chambers. The fluid compressed by the compressor may be inthe form of combustion air or an air/fuel mixture.

[0003] An internal combustion engine may also include a superchargerarranged in series with a turbocharger compressor of an engine. U.S.Pat. No. 6,273,076 (Beck et al., issued Aug. 14, 2001) discloses asupercharger having a turbine that drives a compressor to increase thepressure of air flowing to a turbocharger compressor of an engine. Insome situations, the air charge temperature may be reduced below ambientair temperature by an early closing of the intake valve.

[0004] Early or late closing of the intake valve, referred to as the“Miller Cycle,” may reduce the effective compression ratio of thecylinder, which in turn reduces compression temperature, whilemaintaining a high expansion ratio. Consequently, a Miller cycle enginemay have improved thermal efficiency and reduced exhaust emissions of,for example, oxides of Nitrogen (NO_(X)). Reduced NO_(X) emissions aredesirable. In a conventional Miller cycle engine, the timing of theintake valve close is typically shifted slightly forward or backwardfrom that of the typical Otto cycle engine. For example, in the Millercycle engine, the intake valve may remain open until the beginning ofthe compression stroke.

[0005] While a turbocharger may utilize some energy from the engineexhaust, the series supercharger/turbocharger arrangement does notutilize energy from the turbocharger exhaust. Furthermore, thesupercharger requires an additional energy source.

[0006] The present invention is directed to overcoming one or more ofthe problems as set forth above.

SUMMARY OF THE INVENTION

[0007] According to one exemplary aspect of the invention, a method ofoperating an internal combustion engine, including at least one cylinderand a piston slidable in the cylinder, is provided. The method mayinclude supplying pressurized air from an intake manifold to an airintake port of a combustion chamber in the cylinder, selectivelyoperating an air intake valve to open the air intake port to allowpressurized air to flow between the combustion chamber and the intakemanifold substantially during a majority portion of a compression strokeof the piston, and operably controlling a fuel supply system to injectfuel into the combustion chamber after the intake valve is closed.

[0008] According to another exemplary aspect of the invention, avariable compression ratio internal combustion engine may include anengine block defining at least one cylinder, a head connected with theengine block, wherein the head includes an air intake port and anexhaust port, and a piston slidable in each cylinder. A combustionchamber may be defined by the head, the piston, and the cylinder. Theengine may include an air intake valve controllably movable to open andclose the air intake port, an air supply system including at least oneturbocharger fluidly connected to the air intake port, and a fuel supplysystem operable to controllably inject fuel into the combustion chamberat a selected timing. A variable intake valve closing mechanism may beconfigured to keep the intake valve open by selective actuation of thevariable intake valve closing mechanism.

[0009] According to yet another exemplary aspect of the invention, amethod of operating an internal combustion engine, including at leastone cylinder and a piston slidable in the cylinder, is provided. Themethod may include imparting rotational movement to a first turbine anda first compressor of a first turbocharger with exhaust air flowing froman exhaust port of the cylinder, and imparting rotational movement to asecond turbine and a second compressor of a second turbocharger withexhaust air flowing from an exhaust duct of the first turbocharger. Themethod may also include compressing air drawn from atmosphere with thesecond compressor, compressing air received from the second compressorwith the first compressor, and supplying pressurized air from the firstcompressor to an air intake port of a combustion chamber in the cylindervia an intake manifold. The method also includes controllably operatinga fuel supply system to inject fuel directly into the combustionchamber, and selectively operating an air intake valve to open the airintake port to allow pressurized air to flow between the combustionchamber and the intake manifold during a portion of a compression strokeof the piston.

[0010] According to still another exemplary aspect of the invention, amethod of controlling an internal combustion engine having a variablecompression ratio is provided. The engine may have a block defining acylinder, a piston slidable in the cylinder, a head connected with theblock, and the piston, the cylinder, and the head defining a combustionchamber. The method may include pressurizing air, supplying the air toan intake manifold, maintaining fluid communication between thecombustion chamber and the intake manifold during a portion of an intakestroke and through a predetermined portion of a compression stroke, andsupplying a pressurized fuel directly to the combustion chamber during aportion of an combustion stroke.

[0011] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate several exemplaryembodiments of the invention and, together with the description, serveto explain the principles of the invention. In the drawings,

[0013]FIG. 1 is a combination diagrammatic and schematic illustration ofan exemplary air supply system for an internal combustion engine inaccordance with the invention;

[0014]FIG. 2 is a combination diagrammatic and schematic illustration ofan exemplary engine cylinder in accordance with the invention;

[0015]FIG. 3 is a diagrammatic sectional view of the exemplary enginecylinder of FIG. 2;

[0016]FIG. 4 is a graph illustrating an exemplary intake valve actuationas a function of engine crank angle in accordance with the presentinvention;

[0017]FIG. 5 is a graph illustrating an exemplary fuel injection as afunction of engine crank angle in accordance with the present invention;

[0018]FIG. 6 is a combination diagrammatic and schematic illustration ofanother exemplary air supply system for an internal combustion engine inaccordance with the invention; and

[0019]FIG. 7 is a combination diagrammatic and schematic illustration ofyet another exemplary air supply system for an internal combustionengine in accordance with the invention.

DETAILED DESCRIPTION

[0020] Reference will now be made in detail to embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

[0021] Referring to FIG. 1, an exemplary air supply system 100 for aninternal combustion engine 110, for example, a four-stroke, dieselengine, is provided. The internal combustion engine 110 includes anengine block 111 defining a plurality of combustion cylinders 112, thenumber of which depends upon the particular application. For example, a4-cylinder engine would include four combustion cylinders, a 6-cylinderengine would include six combustion cylinders, etc. In the exemplaryembodiment of FIG. 1, six combustion cylinders 112 are shown. It shouldbe appreciated that the engine 110 may be any other type of internalcombustion engine, for example, a gasoline or natural gas engine.

[0022] The internal combustion engine 110 also includes an intakemanifold 114 and an exhaust manifold 116. The intake manifold 114provides fluid, for example, air or a fuel/air mixture, to thecombustion cylinders 112. The exhaust manifold 116 receives exhaustfluid, for example, exhaust gas, from the combustion cylinders 112. Theintake manifold 114 and the exhaust manifold 116 are shown as asingle-part construction for simplicity in the drawing. However, itshould be appreciated that the intake manifold 114 and/or the exhaustmanifold 116 may be constructed as multi-part manifolds, depending uponthe particular application.

[0023] The air supply system 100 includes a first turbocharger 120 andmay include a second turbocharger 140. The first and secondturbochargers 120, 140 may be arranged in series with one another suchthat the second turbocharger 140 provides a first stage ofpressurization and the first turbocharger 120 provides a second stage ofpressurization. For example, the second turbocharger 140 may be a lowpressure turbocharger and the first turbocharger 120 may be a highpressure turbocharger. The first turbocharger 120 includes a turbine 122and a compressor 124. The turbine 122 is fluidly connected to theexhaust manifold 116 via an exhaust duct 126. The turbine 122 includes aturbine wheel 128 carried by a shaft 130, which in turn may be rotatablycarried by a housing 132, for example, a single-part or multi-parthousing. The fluid flow path from the exhaust manifold 116 to theturbine 122 may include a variable nozzle (not shown) or other variablegeometry arrangement adapted to control the velocity of exhaust fluidimpinging on the turbine wheel 128.

[0024] The compressor 124 includes a compressor wheel 134 carried by theshaft 130. Thus, rotation of the shaft 130 by the turbine wheel 128 inturn may cause rotation of the compressor wheel 134.

[0025] The first turbocharger 120 may include a compressed air duct 138for receiving compressed air from the second turbocharger 140 and an airoutlet line 152 for receiving compressed air from the compressor 124 andsupplying the compressed air to the intake manifold 114 of the engine110. The first turbocharger 120 may also include an exhaust duct 139 forreceiving exhaust fluid from the turbine 122 and supplying the exhaustfluid to the second turbocharger 140.

[0026] The second turbocharger 140 may include a turbine 142 and acompressor 144. The turbine 142 may be fluidly connected to the exhaustduct 139. The turbine 142 may include a turbine wheel 146 carried by ashaft 148, which in turn may be rotatably carried by the housing 132.The compressor 144 may include a compressor wheel 150 carried by theshaft 148. Thus, rotation of the shaft 148 by the turbine wheel 146 mayin turn cause rotation of the compressor wheel 150.

[0027] The second turbocharger 140 may include an air intake line 136providing fluid communication between the atmosphere and the compressor144. The second turbocharger 140 may also supply compressed air to thefirst turbocharger 120 via the compressed air duct 138. The secondturbocharger 140 may include an exhaust outlet 154 for receiving exhaustfluid from the turbine 142 and providing fluid communication with theatmosphere. In an embodiment, the first turbocharger 120 and secondturbocharger 140 may be sized to provide substantially similarcompression ratios. For example, the first turbocharger 120 and secondturbocharger 140 may both provide compression ratios of between 2 to 1and 3 to 1, resulting in a system compression ratio of at least 4:1 withrespect to atmospheric pressure. Alternatively, the second turbocharger140 may provide a compression ratio of 3 to 1 and the first turbocharger120 may provide a compression ratio of 1.5 to 1, resulting in a systemcompression ratio of 4.5 to 1 with respect to atmospheric pressure.

[0028] The air supply system 100 may include an air cooler 156, forexample, an aftercooler, between the compressor 124 and the intakemanifold 114. The air cooler 156 may extract heat from the air to lowerthe intake manifold temperature and increase the air density.Optionally, the air supply system 100 may include an additional aircooler 158, for example, an intercooler, between the compressor 144 ofthe second turbocharger 140 and the compressor 124 of the firstturbocharger 120. Alternatively, the air supply system 100 mayoptionally include an additional air cooler (not shown) between the aircooler 156 and the intake manifold 114. The optional additional aircooler may further reduce the intake manifold temperature.

[0029] Referring now to FIG. 2, a cylinder head 211 may be connectedwith the engine block 111. Each cylinder 112 in the cylinder head 211may be provided with a fuel supply system 202. The fuel supply system202 may include a fuel port 204 opening to a combustion chamber 206within the cylinder 112. The fuel supply system 202 may inject fuel, forexample, diesel fuel, directly into the combustion chamber 206.

[0030] The cylinder 112 may contain a piston 212 slidably movable in thecylinder. A crankshaft 213 may be rotatably disposed within the engineblock 111. A connecting rod 215 may couple the piston 212 to thecrankshaft 213 so that sliding motion of the piston 212 within thecylinder 112 results in rotation of the crankshaft 213. Similarly,rotation of the crankshaft 213 results in a sliding motion of the piston212. For example, an uppermost position of the piston 212 in thecylinder 112 corresponds to a top dead center position of the crankshaft213, and a lowermost position of the piston 212 in the cylinder 112corresponds to a bottom dead center position of the crankshaft 213.

[0031] As one skilled in the art will recognize, the piston 212 in aconventional, four-stroke engine cycle reciprocates between theuppermost position and the lowermost position during a combustion (orexpansion) stroke, an exhaust stroke, and intake stroke, and acompression stroke. Meanwhile, the crankshaft 213 rotates from the topdead center position to the bottom dead center position during thecombustion stroke, from the bottom dead center to the top dead centerduring the exhaust stroke, from top dead center to bottom dead centerduring the intake stroke, and from bottom dead center to top dead centerduring the compression stroke. Then, the four-stroke cycle begins again.Each piston stroke correlates to about 180° of crankshaft rotation, orcrank angle. Thus, the combustion stroke may begin at about 0° crankangle, the exhaust stroke at about 180°, the intake stroke at about360°, and the compression stroke at about 540°.

[0032] The cylinder 112 may include at least one intake port 208 and atleast one exhaust port 210, each opening to the combustion chamber 206.The intake port 208 may be opened and closed by an intake valve assembly214, and the exhaust port 210 may be opened and closed by an exhaustvalve assembly 216. The intake valve assembly 214 may include, forexample, an intake valve 218 having a head 220 at a first end 222, withthe head 220 being sized and arranged to selectively close the intakeport 208. The second end 224 of the intake valve 218 may be connected toa rocker arm 226 or any other conventional valve-actuating mechanism.The intake valve 218 may be movable between a first position permittingflow from the intake manifold 114 to enter the combustion cylinder 112and a second position substantially blocking flow from the intakemanifold 114 to the combustion cylinder 112. A spring 228 may bedisposed about the intake valve 218 to bias the intake valve 218 to thesecond, closed position.

[0033] A camshaft 232 carrying a cam 234 with one or more lobes 236 maybe arranged to operate the intake valve assembly 214 cyclically based onthe configuration of the cam 234, the lobes 236, and the rotation of thecamshaft 232 to achieve a desired intake valve timing. The exhaust valveassembly 216 may be configured in a manner similar to the intake valveassembly 214 and may be operated by one of the lobes 236 of the cam 234.In an embodiment, the intake lobe 236 may be configured to operate theintake valve 218 in a conventional Otto or diesel cycle, whereby theintake valve 218 moves to the second position from between about 10°before bottom dead center of the intake stroke and about 10° afterbottom dead center of the compression stroke. Alternatively, the intakevalve assembly 214 and/or the exhaust valve assembly 216 may be operatedhydraulically, pneumatically, electronically, or by any combination ofmechanics, hydraulics, pneumatics, and/or electronics.

[0034] The intake valve assembly 214 may include a variable intake valveclosing mechanism 238 structured and arranged to selectively interruptcyclical movement of and extend the closing timing of the intake valve218. The variable intake valve closing mechanism 238 may be operatedhydraulically, pneumatically, electronically, mechanically, or anycombination thereof. For example, the variable intake valve closingmechanism 238 may be selectively operated to supply hydraulic fluid, forexample, at a low pressure or a high pressure, in a manner to resistclosing of the intake valve 218 by the bias of the spring 228. That is,after the intake valve 218 is lifted, i.e., opened, by the cam 234, andwhen the cam 234 is no longer holding the intake valve 218 open, thehydraulic fluid may hold the intake valve 218 open for a desired period.The desired period may change depending on the desired performance ofthe engine 110. Thus, the variable intake valve closing mechanism 238enables the engine 110 to operate under a conventional Otto or dieselcycle or under a variable late-closing Miller cycle.

[0035] As shown in FIG. 4, the intake valve 218 may begin to open atabout 360° crank angle, that is, when the crankshaft 213 is at or near atop dead center position of an intake stroke 406. The closing of theintake valve 218 may be selectively varied from about 540° crank angle,that is, when the crank shaft is at or near a bottom dead centerposition of a compression stroke 407, to about 650° crank angle, thatis, about 70° before top center of the combustion stroke 508. Thus, theintake valve 218 may be held open for a majority portion of thecompression stroke 407, that is, for the first half of the compressionstroke 407 and a portion of the second half of the compression stroke407.

[0036] The fuel supply system 202 may include a fuel injector assembly240, for example, a mechanically-actuated, electronically-controlledunit injector, in fluid communication with a common fuel rail 242.Alternatively, the fuel injector assembly 240 may be any common railtype injector and may be actuated and/or operated hydraulically,mechanically, electrically, piezo-electrically, or any combinationthereof. The common fuel rail 242 provides fuel to the fuel injectorassembly 240 associated with each cylinder 112. The fuel injectorassembly 240 may inject or otherwise spray fuel into the cylinder 112via the fuel port 204 in accordance with a desired timing.

[0037] A controller 244 may be electrically connected to the variableintake valve closing mechanism 238 and/or the fuel injector assembly240. The controller 244 may be configured to control operation of thevariable intake valve closing mechanism 238 and/or the fuel injectorassembly 240 based on one or more engine conditions, for example, enginespeed, load, pressure, and/or temperature in order to achieve a desiredengine performance. It should be appreciated that the functions of thecontroller 244 may be performed by a single controller or by a pluralityof controllers. Similarly, spark timing in a natural gas engine mayprovide a similar function to fuel injector timing of a compressionignition engine.

[0038] Referring now to FIG. 3, each fuel injector assembly 240 may beassociated with an injector rocker arm 250 pivotally coupled to a rockershaft 252. Each fuel injector assembly 240 may include an injector body254, a solenoid 256, a plunger assembly 258, and an injector tipassembly 260. A first end 262 of the injector rocker arm 250 may beoperatively coupled to the plunger assembly 258. The plunger assembly258 may be biased by a spring 259 toward the first end 262 of theinjector rocker arm 250 in the general direction of arrow 296.

[0039] A second end 264 of the injector rocker arm 250 may beoperatively coupled to a camshaft 266. More specifically, the camshaft266 may include a cam lobe 267 having a first bump 268 and a second bump270. The camshafts 232, 266 and their respective lobes 236, 267 may becombined into a single camshaft (not shown) if desired. The bumps 268,270 may be moved into and out of contact with the second end 264 of theinjector rocker arm 250 during rotation of the camshaft 266. The bumps268, 270 may be structured and arranged such that the second bump 270may provide a pilot injection of fuel at a predetermined crank anglebefore the first bump 268 provides a main injection of fuel. It shouldbe appreciated that the cam lobe 267 may have only a first bump 268 thatinjects all of the fuel per cycle.

[0040] When one of the bumps 268, 270 is rotated into contact with theinjector rocker arm 250, the second end 264 of the injector rocker arm250 is urged in the general direction of arrow 296. As the second end264 is urged in the general direction of arrow 296, the rocker arm 250pivots about the rocker shaft 252 thereby causing the first end 262 tobe urged in the general direction of arrow 298. The force exerted on thesecond end 264 by the bumps 268, 270 is greater in magnitude than thebias generated by the spring 259, thereby causing the plunger assembly258 to be likewise urged in the general direction of arrow 298. When thecamshaft 266 is rotated beyond the maximum height of the bumps 268, 270,the bias of the spring 259 urges the plunger assembly 258 in the generaldirection of arrow 296. As the plunger assembly 258 is urged in thegeneral direction of arrow 296, the first end 262 of the injector rockerarm 250 is likewise urged in the general direction of arrow 296, whichcauses the injector rocker arm 250 to pivot about the rocker shaft 252thereby causing the second end 264 to be urged in the general directionof arrow 298.

[0041] The injector body 254 defines a fuel port 272. Fuel, such asdiesel fuel, may be drawn or otherwise aspirated into the fuel port 272from the fuel rail 242 when the plunger assembly 258 is moved in thegeneral direction of arrow 296. The fuel port 272 is in fluidcommunication with a fuel valve 274 via a first fuel channel 276. Thefuel valve 274 is, in turn. in fluid communication with a plungerchamber 278 via a second fuel channel 280.

[0042] The solenoid 256 may be electrically coupled to the controller244 and mechanically coupled to the fuel valve 274. Actuation of thesolenoid 256 by a signal from the controller 244 may cause the fuelvalve 274 to be switched from an open position to a closed position.When the fuel valve 274 is positioned in its open position, fuel mayadvance from the fuel port 272 to the plunger chamber 278, and viceversa. However, when the fuel valve 274 is positioned in its closedpositioned, the fuel port 272 is isolated from the plunger chamber 278.

[0043] The injector tip assembly 260 may include a check valve assembly282. Fuel may be advanced from the plunger chamber 278, through an inletorifice 284, a third fuel channel 286, an outlet orifice 288, and intothe cylinder 112 of the engine 110.

[0044] Thus, it should be appreciated that when one of the bumps 268,270 is not in contact with the injector rocker arm 16, the plungerassembly 258 is urged in the general direction of arrow 296 by thespring 259 thereby causing fuel to be drawn into the fuel port 272 whichin turn fills the plunger chamber 278 with fuel. As the camshaft 266 isfurther rotated, one of the bumps 268, 270 is moved into contact withthe rocker arm 250, thereby causing the plunger assembly 258 to be urgedin the general direction of arrow 298. If the controller 244 is notgenerating an injection signal, the fuel valve 274 remains in its openposition, thereby causing the fuel which is in the plunger chamber 278to be displaced by the plunger assembly 258 through the fuel port 272.However, if the controller 244 is generating an injection signal, thefuel valve 274 is positioned in its closed position thereby isolatingthe plunger chamber 278 from the fuel port 272. As the plunger assembly258 continues to be urged in the general direction of arrow 298 by thecamshaft 266, fluid pressure within the fuel injector assembly 240increases. At a predetermined pressure magnitude, for example, at about5500 psi (38 MPa), fuel is injected into the cylinder 112. Fuel willcontinue to be injected into the cylinder 112 until the controller 244signals the solenoid 256 to return the fuel valve 274 to its openposition.

[0045] As shown in the exemplary graph of FIG. 5, the pilot injection offuel may commence when the crankshaft 213 is at about 675° crank angle,that is, about 45° before top dead center of the compression stroke 407.The main injection of fuel may occur when the crankshaft 213 is at about710° crank angle, that is, about 10° before top dead center of thecompression stroke 407 and about 45° after commencement of the pilotinjection. Generally, the pilot injection may commence when thecrankshaft 213 is about 40-50° before top dead center of the compressionstroke 407 and may last for about 10-15° crankshaft rotation. The maininjection may commence when the crankshaft 213 is between about 10°before top dead center of the compression stroke 407 and about 12° aftertop dead center of the combustion stroke 508. The main injection maylast for about 20-45° crankshaft rotation.

[0046]FIG. 6 is a combination diagrammatic and schematic illustration ofa second exemplary air supply system 300 for the internal combustionengine 110. The air supply system 300 may include a turbocharger 320,for example, a high-efficiency turbocharger capable of producing atleast about a 4 to 1 compression ratio with respect to atmosphericpressure. The turbocharger 320 may include a turbine 322 and acompressor 324. The turbine 322 may be fluidly connected to the exhaustmanifold 116 via an exhaust duct 326. The turbine 322 may include aturbine wheel 328 carried by a shaft 330, which in turn may be rotatablycarried by a housing 332, for example, a single-part or multi-parthousing. The fluid flow path from the exhaust manifold 116 to theturbine 322 may include a variable nozzle (not shown), which may controlthe velocity of exhaust fluid impinging on the turbine wheel 328.

[0047] The compressor 324 may include a compressor wheel 334 carried bythe shaft 330. Thus, rotation of the shaft 330 by the turbine wheel 328in turn may cause rotation of the compressor wheel 334. The turbocharger320 may include an air inlet 336 providing fluid communication betweenthe atmosphere and the compressor 324 and an air outlet 352 forsupplying compressed air to the intake manifold 114 of the engine 110.The turbocharger 320 may also include an exhaust outlet 354 forreceiving exhaust fluid from the turbine 322 and providing fluidcommunication with the atmosphere.

[0048] The air supply system 300 may include an air cooler 356 betweenthe compressor 324 and the intake manifold 114. Optionally, the airsupply system 300 may include an additional air cooler (not shown)between the air cooler 356 and the intake manifold 114.

[0049]FIG. 7 is a combination diagrammatic and schematic illustration ofa third exemplary air supply system 400 for the internal combustionengine 110. The air supply system 400 may include a turbocharger 420,for example, a turbocharger 420 having a turbine 422 and two compressors424, 444. The turbine 422 may be fluidly connected to the exhaustmanifold 116 via an inlet duct 426. The turbine 422 may include aturbine wheel 428 carried by a shaft 430, which in turn may be rotatablycarried by a housing 432, for example, a single-part or multi-parthousing. The fluid flow path from the exhaust manifold 116 to theturbine 422 may include a variable nozzle (not shown), which may controlthe velocity of exhaust fluid impinging on the turbine wheel 428.

[0050] The first compressor 424 may include a compressor wheel 434carried by the shaft 430, and the second compressor 444 may include acompressor wheel 450 carried by the shaft 430. Thus, rotation of theshaft 430 by the turbine wheel 428 in turn may cause rotation of thefirst and second compressor wheels 434, 450. The first and secondcompressors 424, 444 may provide first and second stages ofpressurization, respectively.

[0051] The turbocharger 420 may include an air intake line 436 providingfluid communication between the atmosphere and the first compressor 424and a compressed air duct 438 for receiving compressed air from thefirst compressor 424 and supplying the compressed air to the secondcompressor 444. The turbocharger 420 may include an air outlet line 452for supplying compressed air from the second compressor 444 to theintake manifold 114 of the engine 110. The turbocharger 420 may alsoinclude an exhaust outlet 454 for receiving exhaust fluid from theturbine 422 and providing fluid communication with the atmosphere.

[0052] For example, the first compressor 424 and second compressor 444may both provide compression ratios of between 2 to 1 and 3 to 1,resulting in a system compression ratio of at least 4:1 with respect toatmospheric pressure. Alternatively, the second compressor 444 mayprovide a compression ratio of 3 to 1 and the first compressor 424 mayprovide a compression ratio of 1.5 to 1, resulting in a systemcompression ratio of 4.5 to 1 with respect to atmospheric pressure.

[0053] The air supply system 400 may include an air cooler 456 betweenthe compressor 424 and the intake manifold 114. Optionally, the airsupply system 400 may include an additional air cooler 458 between thefirst compressor 424 and the second compressor 444 of the turbocharger420. Alternatively, the air supply system 400 may optionally include anadditional air cooler (not shown) between the air cooler 456 and theintake manifold 114.

[0054] Industrial Applicability

[0055] During use, the internal combustion engine 110 operates in aknown manner using, for example, the diesel principle of operation.Referring to the exemplary air supply system shown in FIG. 1, exhaustgas from the internal combustion engine 110 is transported from theexhaust manifold 116 through the inlet duct 126 and impinges on andcauses rotation of the turbine wheel 128. The turbine wheel 128 iscoupled with the shaft 130, which in turn carries the compressor wheel134. The rotational speed of the compressor wheel 134 thus correspondsto the rotational speed of the shaft 130.

[0056] The exemplary fuel supply system 200 and cylinder 112 shown inFIG. 2 may be used with each of the exemplary air supply systems 100,300, 400. Compressed air is supplied to the combustion chamber 206 viathe intake port 208, and exhaust air exits the combustion chamber 206via the exhaust port 210. The intake valve assembly 214 and the exhaustvalve assembly 216 may be controllably operated to direct airflow intoand out of the combustion chamber 206.

[0057] In a conventional Otto or diesel cycle mode, the intake valve 218moves from the second position to the first position in a cyclicalfashion to allow compressed air to enter the combustion chamber 206 ofthe cylinder 112 at near top center of the intake stroke 406 (about 360°crank angle), as shown in FIG. 4. At near bottom dead center of thecompression stroke (about 540° crank angle), the intake valve 218 movesfrom the first position to the second position to block additional airfrom entering the combustion chamber 206. Fuel may then be injector fromthe fuel injector assembly 240 at near top dead center of thecompression stroke (about 720° crank angle).

[0058] In a conventional Miller cycle engine, the conventional Otto ordiesel cycle is modified by moving the intake valve 218 from the firstposition to the second position at either some predetermined time beforebottom dead center of the intake stroke 406 (i.e., before 540° crankangle) or some predetermined time after bottom dead center of thecompression stroke 407 (i.e., after 540° crank angle). In a conventionallate-closing Miller cycle, the intake valve 218 is moved from the firstposition to the second position during a first portion of the first halfof the compression stroke 407.

[0059] The variable intake valve closing mechanism 238 enables theengine 110 to be operated in both a late-closing Miller cycle and aconventional Otto or diesel cycle. Further, injecting a substantialportion of fuel after top dead center of the combustion stroke 508, asshown in FIG. 5, may reduce NO_(X) emissions and increase the amount ofenergy rejected to the exhaust manifold 116 in the form of exhaustfluid. Use of a high-efficiency turbocharger 320, 420 or seriesturbochargers 120, 140 may enable recapture of at least a portion of therejected energy from the exhaust. The rejected energy may be convertedinto increased air pressures delivered to the intake manifold 114, whichmay increase the energy pushing the piston 212 against the crankshaft213 to produce useable work. In addition, delaying movement of theintake valve 218 from the first position to the second position mayreduce the compression temperature in the combustion chamber 206. Thereduced compression temperature may further reduce NO_(X) emissions.

[0060] The controller 244 may operate the variable intake valve closingmechanism 238 to vary the timing of the intake valve assembly 214 toachieve desired engine performance based on one or more engineconditions, for example, engine speed, engine load, engine temperature,boost, and/or manifold intake temperature. The variable intake valveclosing mechanism 238 may also allow more precise control of theair/fuel ratio. By delaying closing of the intake valve assembly 214,the controller 244 may control the cylinder pressure during thecompression stroke of the piston 212. For example, late closing of theintake valve reduces the compression work that the piston 212 mustperform without compromising cylinder pressure and while maintaining astandard expansion ratio and a suitable air/fuel ratio.

[0061] The high pressure air provided by the exemplary air supplysystems 100, 300, 400 may provide extra boost on the induction stroke ofthe piston 212. The high pressure may also enable the intake valveassembly 214 to be closed even later than in a conventional Miller cycleengine. In the present invention, the intake valve assembly 214 mayremain open until the second half of the compression stroke of thepiston 212, for example, as late as about 80° to 70° before top deadcenter (BTDC). While the intake valve assembly 214 is open, air may flowbetween the chamber 206 and the intake manifold 114. Thus, the cylinder112 experiences less of a temperature rise in the chamber 206 during thecompression stroke of the piston 212.

[0062] Since the closing of the intake valve assembly 214 may bedelayed, the timing of the fuel supply system may also be retarded. Forexample, the controller 244 may controllably operate the fuel injectorassembly 240 to supply fuel to the combustion chamber 206 after theintake valve assembly 214 is closed. For example, the fuel injectorassembly 240 may be controlled to supply a pilot injection of fuelcontemporaneous with or slightly after the intake valve assembly 214 isclosed and to supply a main injection of fuel contemporaneous with orslightly before combustion temperature is reached in the chamber 206. Asa result, a significant amount of exhaust energy may be available forrecirculation by the air supply system 100, 300, 400, which mayefficiently extract additional work from the exhaust energy.

[0063] Referring to the exemplary air supply system 100 of FIG. 1, thesecond turbocharger 140 may extract otherwise wasted energy from theexhaust stream of the first turbocharger 120 to turn the compressorwheel 150 of the second turbocharger 140, which is in series with thecompressor wheel 134 of the first turbocharger 120. The extrarestriction in the exhaust path resulting from the addition of thesecond turbocharger 140 may raise the back pressure on the piston 212.However, the energy recovery accomplished through the secondturbocharger 140 may offset the work consumed by the higher backpressure. For example, the additional pressure achieved by the seriesturbochargers 120, 140 may do work on the piston 212 during theinduction stroke of the combustion cycle. Further, the added pressure onthe cylinder resulting from the second turbocharger 140 may becontrolled and/or relieved by using the late intake valve closing. Thus,the series turbochargers 120, 140 may provide fuel efficiency via theair supply system 100, and not simply more power

[0064] It should be appreciated that the air cooler 156, 356, 456preceding the intake manifold 114 may extract heat from the air to lowerthe inlet manifold temperature, while maintaining the denseness of thepressurized air. The optional additional air cooler between compressorsor after the air cooler 156, 356, 456 may further reduce the inletmanifold temperature, but may lower the work potential of thepressurized air. The lower inlet manifold temperature may reduce theNO_(X) emissions.

[0065] An air and fuel supply system for an internal combustion enginein accordance with the exemplary embodiments of the invention mayextract additional work from the engine's exhaust. The system may alsoachieve fuel efficiency and reduced NO_(X) emissions, while maintainingwork potential and ensuring that the system reliability meets withoperator expectations.

[0066] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the disclosed air and fuelsupply system for an internal combustion engine without departing fromthe scope or spirit of the invention. Other embodiments of the inventionwill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and examples be considered as exemplaryonly.

What is claimed is:
 1. A method of operating an internal combustionengine including at least one cylinder and a piston slidable in thecylinder, the method comprising: supplying pressurized air from anintake manifold to an air intake port of a combustion chamber in thecylinder; selectively operating an air intake valve to open the airintake port to allow pressurized air to flow between the combustionchamber and the intake manifold substantially during a majority portionof a compression stroke of the piston; and operably controlling a fuelsupply system to inject fuel into the combustion chamber after theintake valve is closed.
 2. The method of claim 1, wherein saidselectively operating includes operating a variable intake valve closingmechanism to keep the intake valve open.
 3. The method of claim 2,wherein the variable intake valve closing mechanism is operated at leastone of hydraulically, pneumatically, mechanically, and electronically.4. The method of claim 1, wherein the selective operation of the airintake valve is based on at least one engine condition.
 5. The method ofclaim 1, wherein said selectively operating includes operating theintake valve to remain open for a portion of a second half of thecompression stroke of the piston.
 6. The method of claim 1, wherein saidoperably controlling a fuel supply system includes operating a fuelinjector assembly at least one of hydraulically, mechanically, andelectronically.
 7. A variable compression ratio internal combustionengine, comprising: an engine block defining at least one cylinder; ahead connected with said engine block, including an air intake port, andan exhaust port; a piston slidable in each cylinder; a combustionchamber being defined by said head, said piston, and said cylinder; anair intake valve controllably movable to open and close the air intakeport; an air supply system including at least one turbocharger fluidlyconnected to the air intake port; a fuel supply system operable tocontrollably inject fuel into the combustion chamber at a selectedtiming; and a variable intake valve closing mechanism configured to keepthe intake valve open by selective operation of the variable intakevalve closing mechanism.
 8. The engine of claim 7, further including anair intake valve assembly connected with said intake valve, said airintake valve assembly adapted to cyclically move said intake valve. 9.The engine of claim 8, wherein said air intake valve assembly includes acam connectable with a rocker arm, said rocker arm being connected withsaid intake valve.
 10. The engine of claim 8, wherein the variableintake valve closing mechanism is operated at least one ofhydraulically, pneumatically, mechanically, and electronically.
 11. Theengine of claim 7, further including a controller configured to operatethe intake valve to remain open for a portion of a second half of acompression stroke.
 12. The engine of claim 7, wherein the fuel supplysystem includes a fuel injector assembly.
 13. The engine of claim 12,wherein the fuel injector assembly is operated at least one ofhydraulically, mechanically, and electronically.
 14. The engine of claim7, wherein the air supply system includes a second turbocharger arrangedin series with the at least one turbocharger.
 15. The engine of claim 7,wherein the at least one turbocharger includes a turbine and twocompressors.
 16. The engine of claim 7, wherein the at least oneturbocharger has a pressure ratio of at least 4:1 with respect toatmospheric pressure.
 17. A method of operating an internal combustionengine including at least one cylinder and a piston slidable in thecylinder, the method comprising: imparting rotational movement to afirst turbine and a first compressor of a first turbocharger withexhaust air flowing from an exhaust port of the cylinder; impartingrotational movement to a second turbine and a second compressor of asecond turbocharger with exhaust air flowing from an exhaust duct of thefirst turbocharger; compressing air drawn from atmosphere with thesecond compressor; compressing air received from the second compressorwith the first compressor; supplying pressurized air from the firstcompressor to an air intake port of a combustion chamber in the cylindervia an intake manifold; controllably operating a fuel supply system toinject fuel directly into the combustion chamber; and selectivelyoperating an air intake valve to open the air intake port to allowpressurized air to flow between the combustion chamber and the intakemanifold during a portion of a compression stroke of the piston.
 18. Themethod of claim 17, wherein fuel is injected during an combustionstroke.
 19. The method of claim 18, wherein fuel injection begins duringthe compression stroke.
 20. The method of claim 17, wherein saidselectively operating includes operating a variable intake valve closingmechanism to interrupt cyclical movement of the intake valve.
 21. Themethod of claim 17, wherein the selective operation of the air intakevalve is based on at least one engine condition.
 22. The method of claim17, wherein said selectively operating includes operating the intakevalve to remain open for a portion of a second half of the compressionstroke of the piston.
 23. The method of claim 17, wherein saidcontrollably operating a fuel supply system includes operating a fuelinjector assembly at least one of hydraulically, mechanically, andelectronically.
 24. An internal combustion engine, comprising: a blockdefining at least one cylinder; a head connected with said block, saidhead having an air intake port and an exhaust port; a piston slidable ineach cylinder; an air intake valve controllably movable to open andclose the air intake port; a first turbocharger including a firstturbine coupled with a first compressor, the first turbine being influid communication with the exhaust port, the first compressor being influid communication with the air intake port; a second compressor beingin fluid communication with atmosphere and the first compressor; a fuelsupply system operable to controllably inject fuel into the combustionchamber; and a controller configured to selectively operate the airintake valve to remain open during a portion of a compression stroke ofthe piston.
 25. The engine of claim 24, wherein the controller isconfigured to inject fuel into the combustion chamber during ancombustion stroke.
 26. The engine of claim 24, wherein said secondcompressor is coupled with said first turbine.
 27. The engine of claim24, wherein the controller is configured to operate the intake valve toremain open for a portion of a second half of the compression stroke ofthe piston.
 28. The engine of claim 24, wherein the fuel supply systemincludes a fuel injector assembly.
 29. An internal combustion engine,comprising: a block defining at least one cylinder; a head connectedwith said block, said head having an air intake port and an exhaustport; a piston slidable in each cylinder; an air intake valve assemblyconnectable with a cam assembly to controllably move an intake valve toopen and close the air intake port; a first turbocharger including afirst turbine coupled with a first compressor, the first turbine beingin fluid communication with the exhaust port and an exhaust duct, thefirst compressor being in fluid communication with the air intake port;a second turbocharger including a second turbine coupled with a secondcompressor, the second turbine being in fluid communication with theexhaust duct of the first turbocharger and atmosphere, the secondcompressor being in fluid communication with atmosphere and the firstcompressor; a fuel supply system connectable with a cam assemblyoperable to controllably inject fuel into the combustion chamber; and avariable intake valve mechanism connectable with said air intake valve,said variable intake valve mechanism being adaptable to interruptcyclical movement of said intake valve.
 30. The engine of claim 29,wherein said first turbocharger and said second turbocharger aresimilarly sized.
 31. The engine of claim 29, wherein said cam assemblyfor said fuel system includes a cam lobe having a first bump and asecond bump.
 32. The engine of claim 29, wherein said variable valvemechanism is actuated at least one of hydraulically, pneumatically,mechanically, and electronically.
 33. The engine of claim 29, furtherincluding an air cooler between at least one of said first compressorand said second compressor.
 34. A method of controlling an internalcombustion engine having a variable compression ratio, said enginehaving a block defining a cylinder, a piston slidable in said cylinder,a head connected with said block, said piston, said cylinder, and saidhead defining a combustion chamber, the method comprising: pressurizingair; supplying said air to an intake manifold of the engine; maintainingfluid communication between said combustion chamber and the intakemanifold during a portion of an intake stroke and through apredetermined portion of a compression stroke; and supplying apressurized fuel directly to the combustion chamber during a portion ofan combustion stroke.
 35. The method of claim 34, further includingsupplying the pressurized fuel during a portion of the compressionstroke.
 36. The method of claim 35, wherein supplying the pressurizedfuel includes supplying a pilot injection at a predetermined crank anglebefore a main injection.
 37. The method of claim 36, wherein said maininjection begins during the compression stroke.
 38. The method of claim34, wherein said predetermined portion of the compression stroke is atleast a majority of the compression stroke.
 39. The method of claim 34,wherein said pressurizing includes a first stage of pressurization and asecond stage of pressurization.
 40. The method of claim 39, furtherincluding cooling air between said first stage of pressurization andsaid second stage of pressurization.
 41. The method of claim 34, furtherincluding cooling the pressurized air.
 42. A method of controlling aninternal combustion engine having a variable compression ratio, saidengine having a block defining a cylinder, a piston slidable in saidcylinder, a head connected with said block, said piston, said cylinder,and said head defining a combustion chamber, the method comprising:pressurizing air to a ratio of at least 4:1 with respect to atmosphericpressure; supplying the pressurized air to an intake manifold of theengine; maintaining fluid communication between the combustion chamberand the intake manifold during an intake stroke and a majority of acompression stroke; and supplying a fuel to the combustion chamberduring at least a portion of the remaining compression stroke.
 43. Themethod of claim 42, wherein said majority is at least 90 degrees crankangle after bottom dead center.
 44. The method of claim 42, wherein saidsupplying fuel includes injecting a first portion of fuel apredetermined period prior to injecting a second portion of fuel. 45.The method of claim 44, wherein said injecting the second portion offuel begins during the compression stroke and terminates during acombustion stroke.
 46. The method of claim 44, further including coolingthe air prior to supplying the air to the combustion chamber.